Asbestos is a commercial term applied to a group of silicate minerals which occur in fibrous form. There are six principal asbestos minerals. Of these six minerals, only one, chrysotile asbestos, belongs to the group classified as serpentine asbestos, that is, minerals characterized by long fibers that are serpentine in shape. The chemical composition of chrysotile asbestos may be represented as: Mg.sub.3 (Si.sub.2 O.sub.5)(OH).sub.4 or 3MgO.2SiO.sub.2.H.sub.2 O. The crystalline structure of chrysotile asbestos consists of altering layers of silica and magnesium oxide/hydroxide bound to each other through covalently shared oxygen. These layers are transverse to the fiber axis.
The other varieties of asbestos are silicates of magnesium, iron, calcium, and sodium. These varieties of asbestos belong to the amphibole (straight fiber) group of minerals. About 95% of world production is the chrysotile form of asbestos.
Due to the unique properties of the asbestos minerals, many different kinds of products were developed during the 1940's through the early 1970's that incorporated asbestos fibers for fire resistance, moisture control, and thermal insulation. Many building products, for example, friable thermal insulation, asbestos-cement pipe, asbestos-cement sheet, floor and roof shingles, transite tiles, acoustical plaster, insulation and fire-retardant paper products, and high-temperature insulation, include asbestos fibers. In the overwhelming majority of cases, these products contain the chrysotile form of asbestos.
For a number of years now it has been recognized that many chronic diseases are associated with the inhalation of airborne asbestos fibers. these diseases include lung cancer, chronic fibrosis of the lung lining, and mesothelioma, a rare but fatal cancer of the lungs.
Government agencies have banned the use of certain products containing both chrysotile and amosite asbestos in building construction. There still remains, however, the continuing presence of chrysotile and amosite asbestos-containing materials in many existing buildings as well as the disposition of chrysolite and amosite asbestos-containing materials which were removed from buildings.
Many building owners have chosen to employ additional measures to ensure that asbestos fibers do not enter occupied space. A temporary and inexpensive method is spraying a surface-coating encapsulating material onto chrysotile and/or asbestos-containing materials to lock-in asbestos. This method, however, provides only a temporary remedy.
Another method employed by building owners is to remove completely all chrysotile and/or amosite asbestos-containing materials. However, this method involves a significant amount of time and expense because it requires the buildings to be sealed off, all chrysotile and amosite asbestos-containing materials to be debrided, and all of the debrided chrysotile and/or amosite asbestos-containing materials to be disposed. In addition, many safeguards must be employed to prevent inhalation of airborne asbestos by workers and others in the vicinity of the working area. Furthermore, the disposal of the debrided chrysotile and/or amosite asbestos-containing materials also remains costly.
A number of methods have been proposed for rendering asbestos-containing material less harmful. U.S. Pat. Nos. 5,041,277, 5,258,562 and 5,264,655 to Mirick and Mirick et al. are directed to method and products for converting asbestos to a non-asbestos material. The method of the U.S. Pat. No. 5,041,277 patent requires wetting the asbestos-containing materials with weak organic acids and subsequently rewetting the asbestos-containing materials with additional weak organic acids. This method, although effective, is not efficient in time and cost because it requires successive wetting of asbestos-containing materials.
The methods of the U.S. Pat. Nos. 5,258,562 and 5,264,655 patents require wetting asbestos-containing with an aqueous solution consisting of weak organic acid, such as trifluoroacetic acid, and optionally fluoride ions. Again, although the methods of the Mirick et al. patents may be effective, they are not efficient in cost and time because the disclosed technology requires the conversion process to be repeated as frequently as possible so that the asbestos-containing materials are subjected to successive spraying with acid solution.
It is, therefore, an object of the present invention to provide a composition and method for converting chrysotile and/or amosite asbestos-containing materials to benign materials which overcome the above difficulties generally associated with the prior art.